High resolution optical system

ABSTRACT

The present invention relates to a high resolution optical system. 
     The optical system of the present invention includes, sequentially from an object side, a first lens having a positive refractive power and an object-side surface convex toward the object side; a second lens having a negative refractive power and an upwardly concave upper surface; a third lens having a positive refractive power; a fourth lens having a negative refractive power; a fifth lens having a positive refractive power and an upwardly convex upper surface; and a six lens having a negative refractive power and an upwardly concave upper surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

Claim and incorporate by reference domestic priority application andforeign priority application as follows:

“Cross Reference to Related Application

This application claims the benefit under 35 U.S.C. Section 119 ofKorean Patent Application Serial No. 10-2012-0118915, entitled filedOct. 25, 2012, which is hereby incorporated by reference in its entiretyinto this application.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical system, and moreparticularly, to an optical system that can implement high resolutionusing six lenses.

2. Description of the Related Art

In general, mobile communication means such as mobile communicationterminals, PDA, and smartphones become to have various additionalfunctions in addition to basic communication functions along with theirincreased use and diversification of services provided throughcommunication technology.

In particular, camera modules mounted to the mobile communication meansare in increasing demand as various convergence devices for highdefinition video shooting, automatic focus adjustment, and QR coderecognition in addition to simple photo shooting using a single focus.

Further, as the size of the camera modules is gradually reduced, higherresolution is required, and as the number of pixels of image sensors isgradually increased, high resolution optical systems are required.

And, in recent times, manufacturing costs of the camera modules aregradually reduced along with price cuts of the mobile communicationdevices.

In order to reduce the unit price of the camera module, first, it ismost preferred to reduce manufacturing costs of lens groups constitutingan optical system embedded in the camera module. However, in order tosatisfy the above-mentioned conditions on improvement of resolution, theoptical system should be constituted by applying a glass lens havinghigh optical performance, but it is impossible to reduce themanufacturing costs of the camera module by using several sheets ofexpensive glass lenses.

Further, when employing a plurality of glass lenses to overcome theresolution problem, it is impossible to reduce a weight of the opticalsystem.

RELATED ART DOCUMENT Patent Document

Patent Document 1: Korean Patent Laid-open Publication No. 2011-24872

SUMMARY OF THE INVENTION

Therefore, the present invention has been invented in order to overcomethe above-described disadvantages and problems raised in a conventionalmobile camera optical system and it is, therefore, an object of thepresent invention to provide an optical system that can implement highresolution and reduce manufacturing costs by configuring an opticalsystem using six aspherical plastic lenses.

Further, it is another object of the present invention to provide a highresolution optical system that can implement high resolution andconfigure a compact optical system by properly placing optical power forsix plastic lenses.

In accordance with one aspect of the present invention to achieve theobject, there is provided an optical system including, sequentially froman object side: a first lens having a positive refractive power and anobject-side surface convex toward the object side; a second lens havinga negative refractive power and an upwardly concave upper surface; athird lens having a positive refractive power; a fourth lens having anegative refractive power; a fifth lens having a positive refractivepower and an upwardly convex upper surface; and a six lens having anegative refractive power and an upwardly concave upper surface.

At this time, an aperture stop may be disposed in front of the firstlens or between the first lens and the second lens to block unnecessarylight of the light incident or passing through the optical system.

Further, the optical system satisfies the following ConditionalExpression with respect to conditions of optical power.

|f4/f|22 2.5   [Conditional Expression]

Here, f4 represents a focal length of the fourth lens, and f representsa focal length of the entire optical system.

Further, the optical system satisfies the following ConditionalExpression with respect to conditions of correction of chromaticaberration.

V1-V4<40   [Conditional Expression]

Here, V1 represents an Abbe number of the first lens, and V4 representsan Abbe number of the fourth lens.

Further, the optical system satisfies the following ConditionalExpression with respect to conditions of the shape of the fourth lens.

0.5<OAL/f<2.0   [Conditional Expression]

Here, OAL represents a distance from the vertex of an optical axis to anupper surface of the first lens, and f represents a focal length of theentire optical system.

And, the optical system satisfies the following Conditional Expressionwith respect to conditions of chromatic aberration.

V2<30   [Conditional Expression]

Here, V2 represents an Abbe number of the second lens.

Further, the first to sixth lenses may be formed of plastic lenses, andat least one of both surfaces of the first to sixth lenses may be formedas an aspherical surface. Preferably, the both surfaces of the first tosixth lenses may be formed as aspherical surfaces.

Further, an optical filter, which consists of a cover glass coated withan infrared cut filter for blocking excessive infrared rays included inlight introduced from the outside, may be further included between thesix lens and an image surface.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1 is a configuration diagram showing lens arrangement of an opticalsystem in accordance with a first embodiment of the present invention;

FIG. 2 is an aberration diagram of the optical system shown in Table 1and FIG. 1;

FIG. 3 is a configuration diagram showing lens arrangement of an opticalsystem in accordance with a second embodiment of the present invention;

FIG. 4 is an aberration diagram of the optical system shown in Table 3and FIG. 3;

FIG. 5 is a configuration diagram showing lens arrangement of an opticalsystem in accordance with a third embodiment of the present invention;and

FIG. 6 is an aberration diagram of the optical system shown in Table 5and FIG. 5.

DETAILED DESCRIPTION OF THE PREFERABLE EMBODIMENTS

A matter regarding to an operation effect including a technicalconfiguration for an object of an optical system in accordance with thepresent invention to achieve the object will be clearly appreciatedthrough the following detailed description with reference to theaccompanying drawings illustrating preferable embodiments of the presentinvention.

However, in the following lens configuration diagram of each embodiment,the thickness, size, and shape of lenses may be somewhat exaggerated fordetailed description of the present invention. Particularly, the shapeof a spherical surface or an aspherical surface shown in the lensconfiguration diagram is shown as an example and not limited thereto.

First, FIG. 1 is a lens configuration diagram showing an embodiment ofan optical system in accordance with the present invention. As shown, ahigh resolution optical system of the present embodiment may include afirst lens L1 having a positive refractive power, a second lens L2having a negative refractive power, a third lens L3 having a positiverefractive power, a fourth lens L4 having a negative refractive power, afifth lens L5 having a positive refractive power, and a sixth lens L6having a negative refractive power.

At this time, as for the shape of the lenses constituting the opticalsystem, the first lens L1 may have a shape in which an object-sidesurface is convex toward an object, the second lens L2 may have a shapein which an upper surface is concave upward, the fifth lens L5 may havea shape in which an upper surface is convex upward, and the sixth lensL6 may have a shape in which an upper surface is concave upward.

Further, an optical filter OF, which consists of an infrared filter forblocking excessive infrared rays included in light passing through theoptical system or a cover glass coated with the infrared filter, may beprovided between the sixth lens L6 and an image surface 15.

Further, in the optical system of the present invention, all of thefirst to sixth lenses L1 to L6 may be formed of plastic lenses, and oneor both surfaces of the first to sixth lenses L1 to L6 may be formed asaspherical surfaces.

The reason for forming at least one of the both surfaces of the firstlens L1 and the second lens L2 of the lenses, which constitute theoptical system in accordance with the present invention, as anaspherical surface is to improve a degree of freedom in design forfacilitating correction of aberrations including chromatic aberrationand mitigating manufacturing tolerances. Further, the reason for formingall of the first to sixth lens L1 to L6 with plastic lenses is toconfigure an optical system that can be used in mobile devices byachieving a light weight even though the optical system consists of aplurality of lenses due to characteristics of the optical system havingeasiness in manufacture of aspherical surfaces compared to glass lensesand mainly mounted to the mobile devices.

Meanwhile, as mentioned above, the optical system of the presentinvention can perform aberration correction and achieve miniaturizationwhile using a plurality of lenses by the following ConditionalExpressions 1 and 4. Operational effects of Conditional Expressions willbe described below.

|f4/f|<2.5   [Conditional Expression 1]

Here, f4 represents a focal length of the fourth lens, and f representsa focal length of the entire optical system.

Conditional Expression 1 relates to conditions of optical power of thefourth lens and the entire optical system. It is possible to make theentire optical system compact by adjusting a refractive power of thefourth lens by Conditional Expression 1. At this time, when deviatingfrom a lower limit of Conditional Expression 1, since it is difficult tosecure performance of resolution of a peripheral portion of the lens dueto an increase in negative power of the fourth lens, a length of theentire optical system may be increased to compensate for this.

V1-V4<40   [Conditional Expression 2]

Here, V1 represents an Abbe number of the first lens, and V4 representsan Abbe number of the fourth lens.

Conditional Expression 2 relates to conditions of correction ofchromatic aberration of the optical system. When deviating from a lowerlimit of Conditional Expression 2, it may be impossible to implementhigh resolution of the entire optical system due to a difficulty incorrection of chromatic aberration.

0.5<OAL<f<2.0   [Conditional Expression 3]

Here, OAL represents a distance from the vertex of an optical axis to anupper surface of the first lens, and f represents a focal length of theentire optical system.

Conditional Expression 3 relates to conditions of the shape of lenses ofthe optical system. When deviating from a lower limit of ConditionalExpression 3, since it is not possible to secure a proper field of viewof the optical system, the field of view is reduced. When exceeding anupper limit, since the entire length of the optical system is increased,it is not possible to configure a compact optical system.

V2<30   [Conditional Expression 4]

Here, V2 represents an Abbe number of the second lens.

Conditional Expression 4 relates to conditions of chromatic aberrationof the optical system. When deviating from a lower limit of ConditionalExpression 4, it is impossible to implement high resolution of theentire optical system due to a difficulty in correction of chromaticaberration.

Hereinafter, a compact wide-angle optical system in accordance with thepresent invention will be described in detail with reference to specificnumerical embodiments.

As described above, all of the following first to third embodiments mayinclude a first lens L1 having a positive refractive power and anobject-side surface convex toward an object side; a second lens L2having a negative refractive power and an upwardly concave uppersurface; a third lens L3 having a positive refractive power; a fourthlens L4 having a negative refractive power; a fifth lens L5 having apositive refractive power and an upwardly convex upper surface; and asixth lens L6 having a negative refractive power and an upwardly concaveupper surface, and an optical filter OF, which consists of an infraredfilter or a cover glass coated with the infrared filter, may be providedbetween the sixth lens L6 and an image surface 15.

Further, an aperture stop (AS) may be installed in the first lens L1 orbetween the first lens L1 and the second lens L2 to block unnecessarylight incident on the optical system.

Further, the first to sixth lenses L1 to L6 may be formed of plasticlenses, and one of both surfaces of the first to sixth lenses L1 to L6may be formed as an aspherical surface.

Meanwhile, an aspherical surface used in each of the followingembodiments is obtained from known Equation 1, and E and a numberfollowing the E used in a Conic constant K and aspherical coefficientsA, B, C, D, E, and F represent a 10's power. For example, E+02represents 10², and E-02represents 10⁻².

$\begin{matrix}{Z = {\frac{c\; Y^{2}}{1 + \sqrt{1 - {( {1 + K} )c^{2}Y^{2}}}} + {A\; Y^{4}} + {B\; Y^{6}} + {C\; Y^{8}} + {D\; Y^{10}} + {E\; Y^{12}} + {F\; Y^{14}} + \ldots}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

Here, Z: distance from vertex of lens in the direction of optical axis

-   -   Y: distance in the direction perpendicular to optical axis    -   c: reciprocal of radius of curvature (r) at vertex of lens    -   K: Conic constant    -   A, B, C, D, E, F: aspherical coefficients

First Embodiment

The following Table 1 shows numerical examples according to the firstembodiment of the present invention.

Further, FIG. 1 is a configuration diagram showing lens arrangement ofan optical system in accordance with the first embodiment of the presentinvention, and FIG. 2 shows an aberration diagram of the optical systemshown in Table 1 and FIG. 1.

In the first embodiment, an effective focal length (F) of the entireoptical system is 4.3 mm, a distance (OAL) from the vertex of an opticalaxis to an upper surface of the first lens is 5.449 mm, and a field ofview (FOV) is 67.7°.

Further, a focal length of the first lens L1 is 3.185 mm, a focal lengthof the second lens L2 is −5.089 mm, a focal length of the third lens is19.79 mm, a focal length of the fourth lens L4 is −23.459 mm, a focallength of the fifth lens L5 is 2.067 mm, and a focal length of the sixthlens L6 is −2.054 mm.

At this time, all of the first to sixth lenses L1 to L6 may be formed ofplastic lenses.

TABLE 1 Abbe Surface Radius of Thickness Refractive Number No. Curvature(R) (mm) Index (n) (v) Remarks *1 1.794 0.62 1.544 56.1 First lens *2−51.128 0.13 *3 4.935 0.30 1.632 23.4 Second lens *4 1.914 0.37 *516.281 0.30 1.544 56.1 Third lens *6 −32.007 0.15 *7 −8.518 0.30 1.63223.4 Fourth lens *8 −20.000 0.27 *9 −3.451 0.87 1.544 56.1 Fifth lens*10  −0.927 0.10 *11  14.414 0.56 1.544 56.1 Sixth lens *12  1.027 0.3213 ∞ 0.30 1.517 64.2 Optical filter 14 ∞ 0.85

In Table 1, the * sign in front of the surface No. represents anaspherical surface. In the first embodiment, one or both surfaces of thefirst to sixth lenses L1 to L6 are aspherical surfaces.

Further, values of aspherical coefficients of the first embodiment byEquation 1 are as in the following Table 2.

TABLE 2 Surface No. K A B C D E 1 0 0.00080 −0.00550 0.01344 −0.01904 02 0 −0.06313 0.13673 0.15630 0.04743 0 3 0 −0.18849 0.33976 −0.357570.05301 −0.00906 4 0 −0.17307 0.28346 −0.24419 0.95736 0 5 0 −0.091300.03735 −0.00227 −0.01159 0 6 0 0.03190 0.03715 −0.02333 0.00066 0 7 0−0.01121 0.00585 −0.00030 −0.00260 0 8 0 −0.02243 0.00251 −0.000280.00110 0 9 −14.81500 −0.05738 0.04788 −0.03246 0.01215 −0.00181 10−3.85011 −0.08732 0.06137 −0.03202 0.01081 −1.44E−03 11 0 −0.03276−0.00422 −0.00374 −0.00065  3.65E−03 12 −6.73354 −0.04177 0.00844−0.00187 0.00022 −1.13E−05

Second Embodiment

The following Table 3 shows numerical examples according to the secondembodiment of the present invention.

Further, FIG. 3 is a configuration diagram showing lens arrangement ofan optical system in accordance with the second embodiment of thepresent invention, and FIG. 4 shows an aberration diagram of the opticalsystem shown in Table 3 and FIG. 3.

In the second embodiment, an effective focal length (F) of the entireoptical system is 4.5 mm, a distance (OAL) from the vertex of an opticalaxis to an upper surface of the first lens is 5.592 mm, and a field ofview (FOV) is 65.3°.

Further, a focal length of the first lens L1 is 3.144 mm, a focal lengthof the second lens L2 is −4.836 mm, a focal length of the third lens L3is 20.064 mm, a focal length of the fourth lens L4 is −48.537 mm, afocal length of the fifth lens L5 is 2.328 mm, and a focal length of thesixth lens L6 is −2.157 mm.

At this time, all of the first to sixth lenses L1 to L6 may be formed ofplastic lenses.

TABLE 3 Surface Radius of Thickness Refractive Abbe No. Curvature (R)(mm) Index (n) Number Remarks *1 1.839 0.68 1.544 56.1 First lens *2−22.721 0.12 *3 5.344 0.30 1.632 23.4 Second lens *4 1.915 0.33 *5−24.900 0.31 1.544 56.1 Third lens *6 −7.647 0.18 *7 −12.088 0.30 1.63223.4 Fourth lens *8 −20.000 0.37 *9 −3.264 0.81 1.544 56.1 Fifth lens*10  −0.995 0.11 *11  −304.909 0.62 1.544 56.1 Sixth lens *12  1.1840.29 13 ∞ 0.30 1.517 64.2 Optical filter 14 ∞ 0.85 In Table 3, the *sign in front of the surface No. represents an aspherical surface. Inthe second embodiment, one or both of the first to sixth lenses L1 to L6are aspherical surfaces.

Further, values of aspherical coefficients of the second embodiment byEquation 1 are as in the following Table 4.

TABLE 4 Surface No. K A B C D E 1 0 0.00141 −0.00889 0.01567 −0.01664 02 0 −0.05635 0.13584 0.15710 0.04960 0 3 0 −0.18277 0.34510 −0.359770.14880 −0.00883 4 0 −0.17854 0.28954 −0.24213 0.09009 0 5 0 −0.093260.04705 −0.00190 −0.01416 0 6 0 −0.03383 0.03559 −0.02350 0.00068 0 7 0−0.01421 0.00209 −0.00056 −0.00134 0 8 0 −0.02287 0.00331 −0.000450.00087 0 9 −12.78900 −0.06441 0.04598 −0.03273 0.01200 −0.00192 10−3.78835 −0.08652 0.06057 −0.03270 0.01074 −1.38E−03 11 0 −0.03082−0.00353 0.00377 −0.00065  3.54E−05 12 −733606 −0.04270 0.00911 −0.001920.00022 −1.03E−05

Third Embodiment

The following Table 5 shows numerical examples according to the thirdembodiment of the present invention.

Further, FIG. 5 is a configuration diagram showing lens arrangement ofan optical system in accordance with the third embodiment of the presentinvention, and FIG. 6 shows an aberration diagram of the optical systemshown in Table 5 and FIG. 5.

In the third embodiment, an effective focal length (F) of the entireoptical system is 4.37 mm, a distance (OAL) from the vertex of anoptical axis to an upper surface of the first lens is 5.684 mm, and afield of view (FOV) is 67.4°.

Further, a focal length of the first lens L1 is 3.089 mm, a focal lengthof the second lens L2 is −4.363 mm, a focal length of the third lens L3is 9.937 mm, a focal length of the fourth lens L4 is −14.406 mm, a focallength of the fifth lens L5 is 2.136 mm, and a focal length of the sixthlens L6 is −2.141 mm.

At this time, all of the first to sixth lenses L1 to L6 may be formed ofplastic lenses.

TABLE 5 Abbe Surface Radius of Thickness Refractive Number No. Curvature(R) (mm) Index (n) (v) Remarks *1 1.945 0.71 1.544 56.1 First lens *2−11.133 0.11 *3 5.393 0.31 1.632 23.4 Second lens *4 1.796 0.35 *5−192.752 0.39 1.544 56.1 Third lens *6 −5.285 0.12 *7 −5.196 0.32 1.54456.1 Fourth lens *8 −15.612 0.32 *9 −2.895 0.87 1.544 56.1 Fifth lens*10  −0.920 0.10 *11  8.644 0.57 1.544 56.1 Sixth lens *12  1.007 0.3613 ∞ 0.30 1.517 64.2 Optical filter 14 ∞ 0.85 In Table 5, the * sign infront of the surface No. represents an aspherical surface. In the thirdembodiment, one or both surfaces of the first to sixth lenses L1 to L6are aspherical surfaces.

Further, values of aspherical coefficients of the third embodiment byEquation 1 are as in the following Table 6.

TABLE 6 Surface No. K A B C D E 1 0 0.00051 −0.01481 0.01850 −0.01714 02 0 −0.04903 0.13616 0.16040 0.05199 0 3 0 −0.17566 0.35084 −0.357970.14694 −0.00923 4 0 −0.19005 0.29351 −0.24124 0.08676 0 5 0 −0.096840.04540 −0.00410 −0.01300 0 6 0 −0.03318 0.04118 −0.02075 0.00143 0 7 0−0.01820 0.00061 0.00218 −0.00123 0 8 0 −0.02483 0.00321 −0.001311.54E−05 0 9 −7.32031 −0.04726 0.05039 −0.03290 0.01176 −0.00212 10−3.64537 −0.09621 0.06332 −0.03262 0.010732 −1.33E−03 11 0 −0.04093−0.00257 0.00387 −0.00065  3.33E−05 12 −6.13717 −0.04287 0.00920−0.00184 0.00022 −1.14E−05

Meanwhile, values of Conditional Expressions for the first to thirdembodiments are as in the following Table 7.

TABLE 7 Classification Embodiment 1 Embodiment 2 Embodiment 3 f4/f−5.455581 −10.786 −3.296568 v1-v4 32.7 32.7 0 OAL/f 1.2671427 1.24257651.3006439 v2 23.4 23.4 23.4

As described above, the optical system in accordance with the presentinvention can achieve a light weight as well as reduce manufacturingcosts by forming six lenses with plastic lenses.

Further, the present invention can implement high resolution byimproving efficiency of correction of aberrations including chromaticaberration and minimizing chromatic aberrations.

Further, the present invention can improve a degree of freedom in designby forming both surfaces of six lenses, which constitute an opticalsystem, as aspherical surfaces and manufacture a high resolution opticalsystem by forming all of the first to sixth lenses with plastic lensesto reduce aberration values.

As described above, although the preferable embodiments of the presentinvention have been shown and described, it will be appreciated by thoseskilled in the art that substitutions, modifications and variations maybe made in these embodiments without departing from the principles andspirit of the general inventive concept, the scope of which is definedin the appended claims and their equivalents.

What is claimed is:
 1. A high resolution optical system comprising,sequentially from an object side: a first lens having a positiverefractive power and an object-side surface convex toward the objectside; a second lens having a negative refractive power and an upwardlyconcave upper surface; a third lens having a positive refractive power;a fourth lens having a negative refractive power; a fifth lens having apositive refractive power and an upwardly convex upper surface; and asix lens having a negative refractive power and an upwardly concaveupper surface.
 2. The high resolution optical system according to claim1, wherein an aperture stop is disposed in front of the first lens orbetween the first lens and the second lens.
 3. The high resolutionoptical system according to claim 1, wherein the optical systemsatisfies the following Conditional Expression with respect toconditions of optical power:|f4f|>2.5   [Conditional Expression] here, f4 represents a focal lengthof the fourth lens, and f represents a focal length of the entireoptical system.
 4. The high resolution optical system according to claim1, wherein the optical system satisfies the following ConditionalExpression with respect to conditions of correction of chromaticaberration:V1-V4<40   [Conditional Expression] here, V1 represents an Abbe numberof the first lens, and V4 represents an Abbe number of the fourth lens.5. The high resolution optical system according to claim 1, wherein theoptical system satisfies the following Conditional Expression withrespect to conditions of the shape of the fourth lens:0.5<OAL/f<2.0   [Conditional Expression] here, OAL represents a distancefrom the vertex of an optical axis to an upper surface of the firstlens, and f represents a focal length of the entire optical system. 6.The high resolution optical system according to claim 1, wherein theoptical system satisfies the following Conditional Expression withrespect to conditions of chromatic aberration:V2<30   [Conditional Expression] here, V2 represents an Abbe number ofthe second lens.
 7. The high resolution optical system according toclaim 1, wherein the first to sixth lenses are formed of plastic lenses.8. The high resolution optical system according to claim 7, wherein atleast one or both surfaces of the first to sixth lenses are formed asaspherical surfaces.
 9. The high resolution optical system according toclaim 1, further comprising: an optical filter consisting of a coverglass coated with an infrared cut filter for blocking excessive infraredrays included in light introduced from the outside between the six lensand an image surface.